This invention relates generally to electrostatic discharge effect on input/output circuits and particularly to protection of output circuits of semiconductor devices from damage resulting from electrostatic discharge.
Electrostatic discharge (ESD) can be a source of destruction for semiconductor devices. Various output protection circuits may be used to protect the output circuits from electrostatic discharge damage. To increase the ESD robustness of CMOS output circuits, an extra long N-diffusion layer of approximately two to five micrometers long may be added between the drain contact and the polysilicon gate of NMOSFET output devices. The area of the N diffusion layer can be as large as thirty to fifty percent of the total NMOSFET output devices. This can be a significant cost in area for high density sub-halfmicron CMOS I/O circuits.